Proton nuclear magnetic resonance was used to probe the environment of the intercalant molecule in low dimensional (aeolotropic) solids 3RI-TaS2(NH3)2/3 and 3RII-TaS2(N2H4)4/3, and, specifically to look for phase transitions associated with changes in superlattice geometry. The proton resonance frequency for the intercalated molecules in the temperature interval 200 to 300K indicates that there are different magnetic environments in three temperature domains. (i) There is only one resonance field for molecules in isotropic magnetic environments. (ii) The high- and low-temperature domains (I and III) have molecules in only two different environments, whereas in the middle temperature domain (II) there are at least four different magnetic environments. (iii) The different magnetic environments measured by the ratio of anisotropic to isotropic resonance absorption intensity (rai) indicate that the ratios rai are constants of the sample in domains I and II. (iv) At low temperatures (domain III), rai depends on magnetic field polarisation effects and the temperature treatment of the sample. The authors conclude that the different magnetic environments observed for ammonia and hydrazine appear to be determined by the host, octahedrally coordinate TaS2

Acrivos, J. V.

Handly, N. H.

English

Handly, N. H

Acrivos, Juana Vivó

SJSU ScholarWorks

San Jose State UniversitySJSU ScholarWorksFaculty Publications, Chemistry Chemistry1-1-1984NMR measurements on Intercalated 3R-TaS2.Ix(I=NH3 and N2H4)N. H. HandlyCalifornia Institute of TechnologyJuana Vivó AcrivosSan Jose State University, juana.acrivos@sjsu.eduFollow this and additional works at: https://scholarworks.sjsu.edu/chem_pubPart of the Physical Chemistry CommonsThis Article is brought to you for free and open access by the Chemistry at SJSU ScholarWorks. It has been accepted for inclusion in FacultyPublications, Chemistry by an authorized administrator of SJSU ScholarWorks. For more information, please contact scholarworks@sjsu.edu.Recommended CitationN. H. Handly and Juana Vivó Acrivos. "NMR measurements on Intercalated 3R-TaS2.Ix (I=NH3 and N2H4)" Journal of Physics C:Solid State Physics (1984): L275-L280. doi:10.1088/0022-3719/14/19/007J. Phys. C: Solid State Phys., 17 (1984) L275-L280. Printed in Great Britain LETTER TO THE EDITOR NMR measurements on intercalated 3R-TaS2 · lx (I = NH3 and N2H4)t N H Handly:j: and J V Acrivos§ +California Institute of Technology, Pasadena, CA91125, USA § Trinity College, Cambridge, CB21TQ, UK Received 22 December 1983 Abstract. Proton nuclear magnetic resonance was used to probe the environment of the intercalant molecule in low dimensional (aeolotropic) solids 3RI-TaSz(NHJhJ and 3Ru-TaS2(N2H4)4/3. and, specifically to look for phase transitions associated with changes in superlattice geometry. The proton resonance frequency for the intercalated molecules in the temperature interval 200 to 300 K indicates that there are different magnetic environ­ments in three temperature domains. (i) There is only one resonance field for molecules in isotropic magnetic environments. (ii) The high- and low-temperature domains (I and III) have molecules in only two different environments, whereas in the middle temperature domain (II) there are at least four different magnetic environments. (iii) The different magnetic environments measured by the ratio of anisotropic to isotropic resonance absorp­tion intensity (r.,) indicate that the ratios r., are constants of the sample in domains I and II. (iv) At low temperatures (domain III), r,i depends on magnetic field polarisation effects and the temperature treatment of the sample. We conclude that the different magnetic environ­ments observed for ammonia and hydrazine appear to be determined by the host. octahed­rally coordinated TaS 2 . The phase transitions that are caused by the intercalation of low dimensional solids ( LDS) have important applications leading to new solid catalysts, conductors and battery materials. For this reason there has been recently a concentrated effort directed to determining the parameters which govern reaction (1): L(qh) + xl(g)- Llx(cpz) (1) where cp1 is the pristine initial crystal phase and cpz is the intercalated phase. This is a complex process which involves at least three steps. First Langmuir absorption of the adduct gas must occur; it is followed by chemisorption and finally insertion of the adduct in between the layers produces a phase transition. The understanding of reaction (1) was strengthened by spectroscopic (Beal and Acrivos 1978) and structural measurements by transmission electron microscopy (TEM) of N2H4in situ intercalated TaS2polymorphs. These indicate (Tatlock and Acrivos 1978) that the in-plane translational symmetry is reduced by intercalation in a precise way which depends on the solid and on the temperature and pressure. The periodic lattice distortion ( PLD) describes the dichalco­genide by an empirical formula TyX2y with y ~ 3, where 103 formula units are held t This work is dedicated to Professor R W Vaughan of Cal. Tech., whose untimely death (1978) left a void that has not to this day been filled. The NMR work was done in his laboratory. § To whom all correspondence is to be addressed. Permanent address: San Jose State University, San Jose, CA 95192, USA. 0022-3719/84/090275 + 06 $02.25 © 1984 The Institute of Physics L275 L276 Letter to the Editor together by layers of adduct I. The value of y is accurately determined from the PLD wavevectors which describe the Bloch functions of the partially occupied orbitally degenerate states of the metal or semimetal and give rise to the distortion according to the Jahn-Teller theorem (Hughes 1977, Acrivos 1974). The existence of localised electron states indicated by the PLD have led to transport and infrared spectroscopic measurements (Sarma et a/1982) which allow an estimate of a semiconductor energy gap of the order of half an electron volt in phase rn. The existence of localised para­magnetic states was verified by ESR absorption measurements near 4.2 K (Guy et al 1982). Nuclear magnetic resonance spectroscopy (NMR) and neutron diffraction offer another means for studying these intercalated solids. Both techniques have been used to probe the intercalant molecule and its macro-environment within the crystal, so far yielding information about the mobility of ammonia and the geometries of ammonia and pyridine in 2H-TaS2 (Gamble and Silbernagel1975, Bray and Sauer 1972). The NMR evidence suggests that the ammonia molecule is sensitive to phase changes associated with superlattice formation in intercalated 2H-TaS2• The ability to study phase behaviour in intercalated 1 T-TaS2 at a microscopic level would greatly add to our understanding of these materials. This work reports NMR studies of 3RrTaS2(NH3)2/3 and 3RwTaS2(N2H4)4;3 between 200-300 K (Acrivos 1979, Acrivos et a/1981). The crystals of 1 T-TaS2 used in this work were grown by Meyer et at (1975) and A Beal and S N Nulsen (Sarma et a/1982). The NMR samples were prepared by placing a single crystal in a flattened tube to facilitate rotational studies which was then connected to a vacuum line for intercalation. Ammonia and hydrazine were purified prior to exposure to the crystals. Ammonia was condensed on sodium to remove traces of water and then the gas was admitted to the sample. Freeze-dried hydrazine was distilled in situ and then admitted to the sample. The ammonia pressure was 700 Torr and the hydrazine vapour pressure was 12 Torr. After one week at room temperature, the sample tube was immersed in liquid nitrogen and the tube sealed by melting the glass. The spectra were collected at 56.4 and 13.1 MHz. Free induction decays were collected for time averaging and were then Fourier transformed to give the absorption spectra. Temperature in the probe was varied and regulated to within ±0.5 oc of the desired value by heating nitrogen gas. Resonance frequency assignments were facilitated with the use of an acetyl chloride reference with an accuracy of± 10Hz. Over the 200-300 K range studied there were three kinds of spectra for 3Rr TaS2(NH3) 213 which define three temperature domains. Evidence of the three domains were also found in the spectra of 3Rn-TaS2(N2H4)4;3 which were qualitatively the same as the spectra of ammonia intercalated 1 T-TaS2 . Two resonance lines were found in domain I (250-300 K). The resonance position of one was insensitive to crystal orientation in the magnetic field while the position of the other line was determined by the angle between the crystal c axis and static magnetic field vector H. The separation in frequency of the anisotropic and isotropic signals could be approximated by the relation v. - v; = 1. 5 A cos2 8 where v. and V; are line positions in Hz, 1.5 A is the maximum separation in Hz and 8 is the angle between the crystal c axis and H. Shown in figure 1 are plots of ( v.- Vi) versus efor ammonia and hydrazine intercalated samples. These follow the (3 cos2 8- 1)/2 law for a Knight shift of K = A/56.1 PPM given in table 1. The ratio of intensities of the anisotropic to isotropic NMR absorption (r.;) was also a feature that characterised each temperature domain. In domain/, ra; was a constant of 600 -;:; ~ 300 200 100 -30 30 120 200 100 40 120 180 (deg) Letter to the Editor L277 Figure 1. Frequency separation between the anisotropic and isotropic proton NMR lines in Hz versus 8 in degrees for 3R1-TaS2(NH3)v3 (sample 1) and 3Rn-TaS2(NlH4)4;J. Full circles (e) show collected data with errors in frequency of ±10Hz and in angle of ±3°. The full curve is the plot of 1.5 A cos28, where A is given in table 1. Table 1. Values of 1.5 A at 56.4 MHz (maximum separation in Hz of the anisotropic and isotropic lines) for different temperatures. Multiple lines Sample T > 250 K 250 K > T > 245 K (1) 640 530 300 130 110 260 2.46 t 3R1-TaS2-(NH3)l/3 ± b ( )2 500 400 220 90 360 1.38 t 3Rn-TaS2-(N2H4)4!3 ± b (2) 200 55 3.63 t The error bin stoichiometry is less than ten per cent of x. the sample and not affected by variation of 8 or temperature. That A is proportional to the applied magnetic field was verified by carrying out measurements at v = 56.4 and 13.1 MHz. A representative spectrum of 3R1-TaSz(NH3)2/3 is shown in figure 2(a). In domain II (245-250 K) spectra of 3R1-TaSz(NH3)2/3 were characterised by the presence of at least five lines; one isotropi<.: and three or four anisotropic. For each of the anisotropic absorptions, the separation from the isotropic line follows the A cos2 8 behaviour. A representative spectrum for 8 = oo is shown in figure 2(b). When all the lines collapse at 8 = 90°, the linewidth is equal to that of the isotropic line. As was observed in domain I, the '•i values for all anisotropic lines were constants of the sample. For 3Ru-TaS2(N2H4)4/3 there was an isotropic line and an unresolved manifold of several lines that collapsed at 8 = 90° showing a maximum separation at 8 = 0°. In domain III (200-245 K) there were two lines which showed the orientational dependence observed in domain I. However, there was a striking feature in this tern­C9-C L278 Letter to the Editor (a) -­500Hz (b) 500Hz Figure 2. NMR absorption representative spectra of 3RI-TaS2(NH3)213(sample 1). (a) At room temperature and e= 0°. The anisotropic peak is at the right at higher frequency. The arrow is a 500Hz standard and points to higher frequency. (b) At 250 K and e= 0°. Ho rai TaS2(NH3I213 Sample 1 Sample 2 o-o· a 2 60 b 0.62 0.73 d 0.33 1.35 45° 90" 135° 180" 2.29 0.27 0.89 2.41 1.88 Figure 3. Illustration of how rotation of a sample cooled to a temperature below 245 K affects rat, the ratio of anisotropic to isotropic line intensity, for five different cooling cycles of sample 1 in table 1. A view down the instrument probe is shown to highlight the importance of the angle between the crystal c axis and the magnetic field. The crystal is seen edge-on and is pictured in an exaggerated off-axis position to help distinguish angles e= oo and e= 180°. Letter to the Editor L279 perature domain which was not observed in domains I or II. Each time any samples were cooled, rai would take on randomly two new values that would reversibly intercon­vert as the crystal was rotated through e= 90° ore= 270°. Figure 3 illustrates the change in rai upon rotation and contains pairs of rai values from several coolings. Our work shows that proton NMR of the guest molecules within TX2 is a good probe of the magnetic micro-environments within intercalated complexes. NMR reveals the presence of two micro-environments within the complexes as well as a phase transition at 245-250 K, most likely associated with the change in superlattice geometries observed in that temperature range by other methods. The significant observations are as follows: (i) Crystals intercalated with NH3 and N2H4 both show the same two-line pattern where the position of the low-frequency peak is independent of, and the high-frequency peak is dependent upon, the orientation of the crystal within the magnetic field. The proton linewidths observed are consistent with a rapid reorientation of NH3and N2H4 molecules within the layers. This is in agreement with the measurements made by Silbernagel and Gamble on 2H-TaSz(NH3)x, but in this metallic complex the Knight shift is one order of magnitude greater than for the 3R-TaS2Ix. The different values of A reported in table 1 suggest that the proton Knight shift is determined by the number of adduct molecules in the complex which localises the electron states. (ii) Intercalant adduct molecules do not exchange between the two magnetic environments that are the source of the isotropic and anisotropic peaks as there is no evidence ofexchange broadening or averaging. This means that the molecular complexes are stable within times longer than t = (2.rrA)- 1 or 10-3to 10-4s. We offer the following proposal for the identities of the magnetic environments leading to the two lines. The isotropic signal arises from protons in fractured or poorly ordered domains and the anisotropic resonance is a result of adduct molecules occupying an ordered region where a superlattice exists. Fractures and other crystal defects that would prevent superlattice formation have been observed by a number of investigators (Tatlock and Acrivos 1978), and the intercalation process itself may be responsible for some of these faults. Regard­less of the cause of the crystal disorder, intercalant molecules in these disordered volumes would not be affected by fields oriented with the crystal geometry and, hence, give rise to the isotropic signal. (iii) Evidence for a role of superlattices in forming the anisotropic field is twofold. Wilson et al (1975) have measured bulk susceptibility in 1 T-TaS 2 and found variation of this parameter coincident with different superlattice geometries. Guy et al (1982) have observed similar effects in 3R-TaS2(NzH4)x· Also we find a complex, multiline spectra with one line isotropic and the remainder anisotropic in the 245-250 K region. This is the same temperature range in which Tatlock and Acrivos (1978) observed a super lattice phase transition. In one ofthe materials we have studied, 3Rn-TaSz(N2H4)4;3, our spectra suggest that two or more distinct superlattices may be present within the sample in this temperature range as each superlattice would contribute a different susceptibility field and be revealed as distinct anisotropic lines. (iv) Below 245 K, a two-line (anisotropic and isotropic) NMR signal like the room temperature spectra is found for 3Rn-TaS2(N2H4)4;3; however, a smaller separation between the two lines is observed. This is in agreement with the fact that a different superlattice occurs within these crystals in the 200-245 K range (Tatlock and Acrivos 1978) and that a decrease in carriers reduces the Knight shift. Also, in this temperature range, a new pattern of resonance line intensity is observed. The sum of anisotropic and isotropic line intensities is not altered from that value observed at room temperature, so L280 Letter to the Editor the total number of protons in the sample remains constant within experimental uncer­tainty. Yet two discrete ratios of anisotropic to isotropic line intensities are found, one for each face of the crystal (figure 3), that do not change until the sample is warmed above 245 K. In addition, each cooling event yields a new pair of intensity ratios. The variation in intensities of the two peaks, which is not observed at temperatures above 245 K, presents an interesting problem. To account for this particular situation, we propose a mechanism whereby the formation of the superlattice at low temperature is affected by temperature. Each cooling would appear to lead to varying amounts of this superlattice since crystal defects may be locked in or introduced by the temperature change. The anisotropic line intensity would be influenced by the volume of the crystal where the local magnetic fields cancel. While the temperature effects on relative line intensity are unpredictable, the effects of the magnetic field polarisation are not random. Although we are unable to explain this latter phenomenon, our results suggest that future experiments at higher magnetic fields may be able to shed some understanding on the chiral dependence of the NMR absorption below 245 K for samples cooled in a magnetic field. Transport measurements of samples cooled in a magnetic field may also show this chiral dependence if the above model where local magnetic fields cancel in discommensurate Bloch walls is correct. These were predicted by McMillan (1976) and found recently by TEM (Fung et a/1981). We have shown that proton NMR studies of the intercalant molecule with an octa­hedrally coordinated TaS2 host are able to describe the phase transition near 245 K, which has not been observable by techniques based upon measurements of bulk proper­ties. Additionally, our findings suggest that intercalant adduct molecules such as ammonia and hydrazine are sensitive to local magnetic fields caused by superlattices. The physical significance is that the random potential fields in the adduct layer can affect the motion of electrons in the TaSzlayer. This work was supported in part by NSF DMR 790011 and NATO Grant 1441. J V Acrivos is grateful for a Visiting Fellowship at Trinity College, Cambridge during 1983 and a Sabbatical leave from SJSU. We also thank Miss J Rowe who did the word processing at Trinity College. References Acrivos J V 1974 J. Phys. Chern. 78 2399 - 1979 Physics and Chemistry ofMaterials with a Layer Structure Vol. VI, ed. FLevy (Dordrecht :Reidel). pp 33-98 Acrivos J V, ParkinS S P, Reynolds J R, Code J and Marseglia E 1981 J. Phys. C: Solid State Phys. 14 L34~L357 Beal A Rand Acrivos J V 1978 Phil. Mag. 37 409 Bray D and Sauer E 1972 Solid State Commun. 111239 Fung L, McKernan S, Steeds J Wand Wilson J A 1981 J. Phys. C: Solid State Phys. 14 5417 Gamble F and Silbernagel B 1975 J. Chern. Phys. 63 2544 GuyD P, Friend RH, Harrison M R, Johnson D Cand Sienko MJ1982J. Phys. C: Solid State Phys. 15 L1245 Hughes H P 1977 J. Phys. C: Solid State Phys. 10 L319 McMillan E L 1976 Phys. Rev. B 14 1496 MeyerS R, Howard R, Stewart G, Acrivos J V and Geballe T H 1975 J. Chern. Phys. 62 4411 Sarma M, Beal A, Nulsen Sand Friend R 1982 J. Phys. C: Solid State Phys. 15 477 Tatlock G J and Acrivos J V 1978 Phil. Mag. 38 81 Wilson J, DiSalvo F and Mahajan S 1975 Adv. Phys. 24 117 

NMR measurements on Intercalated 3R-TaS2.Ix (I=NH3 and N2H4)

Caltech Authors - Main

J. Phys. C: Solid State Phys., 17 (1984) L27SL280. Printed in Great Britain 
LETTER TO THE EDITOR 
NMR measurements on intercalated 3R-TaS2 * I, 
(I = NH, and N,H,)T 
N H Handlyt and J V AcrivosP 
$ California Institute of Technology, Pasadena, CA91125, USA 
§ Trinity College, Cambridge, CB2 lTQ, UK 
Received 22 December 1983 
Abstract. Proton nuclear magnetic resonance was used to probe the environment of 
the intercalant molecule in low dimensional (aeolotropic) solids ~ R I - T ~ S ~ ( N H ~ ) L ~  and 
~ R I I - T ~ S ~ ( N ~ H J ) ~ D ,  and, specifically to look for phase transitions associated with changes in 
superlattice geometry. The proton resonance frequency for the intercalated molecules in 
the temperature interval 200 to 300 K indicates that there are different magnetic environ- 
ments in three temperature domains. (i) There is only one resonance field for molecules in 
isotropic magnetic environments. (ii) The high- and low-temperature domains (I and 111) 
have molecules in only two different environments, whereas in the middle temperature 
domain (11) there are at least four different magnetic environments. (iii) The different 
magnetic environments measured by the ratio of anisotropic to isotropic resonance absorp- 
tion intensity (raJ indicate that the ratios rat are constants of the sample in domains I and 11. 
(iv) At low temperatures (domain 111), rat depends on magnetic field polarisation effects and 
the temperature treatment of the sample. We conclude that the different magnetic environ- 
ments observed for ammonia and hydrazine appear to be determined by the host, octahed- 
rally coordinated TaS2. 
The phase transitions that are caused by the intercalation of low dimensional solids (LDS) 
have important applications leading to new solid catalysts, conductors and battery 
materials. For this reason there has been recently a concentrated effort directed to 
determining the parameters which govern reaction (1): 
where q1 is the pristine initial crystal phase and 9 is the intercalated phase. This is a 
complex process which involves at least three steps. First Langmuir absorption of the 
adduct gas must occur; it is followed by chemisorption and finally insertion of the adduct 
in between the layers produces a phase transition. The understanding of reaction (1) 
was strengthened by spectroscopic (Beal and Acrivos 1978) and structural measurements 
by transmission electron microscopy (TEM) of N2H4 in situ intercalated TaS2 polymorphs. 
These indicate (Tatlock and Acrivos 1978) that the in-plane translational symmetry is 
reduced by intercalation in a precise way which depends on the solid and on the 
temperature and pressure. The periodic lattice distortion (PLD) describes the dichalco- 
genide by an empirical formula TyX2y with y 5 3, where lo3 formula units are held 
t This work is dedicated to Professor R W Vaughan of Cal. Tech., whose untimely death (1978) left a void 
that has not to this day been filled. The NMR work was done in his laboratory. 
§ To whom all correspondence is to be addressed. Permanent address: San Jost State University, San Jost ,  
CA 95192, USA. 
0022-3719/84/090275 + 06 $02.25 0 1984 The Institute of Physics L275 
L276 Letter to the Editor 
together by layers of adduct I. The value of y is accurately determined from the PLD 
wavevectors which describe the Bloch functions of the partially occupied orbitally 
degenerate states of the metal or semimetal and give rise to the distortion according to 
the Jahn-Teller theorem (Hughes 1977, Acrivos 1974). The existence of localised 
electron states indicated by the PLD have led to transport and infrared spectroscopic 
measurements (Sarma et a1 1982) which allow an estimate of a semiconductor energy 
gap of the order of half an electron volt in phase p ~ .  The existence of localised para- 
magnetic states was verified by ESR absorption measurements near 4.2 K (Guy et a1 
1982). Nuclear magnetic resonance spectroscopy (NMR) and neutron diffraction offer 
another means for studying these intercalated solids. Both techniques have been used 
to probe the intercalant molecule and its macro-environment within the crystal, so far 
yielding information about the mobility of ammonia and the geometries of ammonia 
and pyridine in 2H-TaS2 (Gamble and Silbernagell975, Bray and Sauer 1972). The NMR 
evidence suggests that the ammonia molecule is sensitive to phase changes associated 
with superlattice formation in intercalated 2H-TaS2. The ability to study phase behaviour 
in intercalated 1T-TaS2 at a microscopic level would greatly add to our understanding 
of these materials. This work reports NMR studies of 3RI-TaS2(NH3)y3 and 
3RII-TaS2(N2H4)4/3 between 200-300 K (Acrivos 1979, Acrivos et a1 1981). 
The crystals of 1T-TaS2 used in this work were grown by Meyer et aZ(1975) and A 
Beal and S N Nulsen (Sarma et aZ1982). The NMR samples were prepared by placing a 
single crystal in a flattened tube to facilitate rotational studies which was then connected 
to a vacuum line for intercalation. Ammonia and hydrazine were purified prior to 
exposure to the crystals. Ammonia was condensed on sodium to remove traces of water 
and then the gas was admitted to the sample. Freeze-dried hydrazine was distilled in situ 
and then admitted to the sample. The ammonia pressure was700 Torr and the hydrazine 
vapour pressure was 12 Torr. After one week at room temperature, the sample tube 
was immersed in liquid nitrogen and the tube sealed by melting the glass. 
The spectra were collected at 56.4 and 13.1 MHz. Free induction decays were 
collected for time averaging and were then Fourier transformed to give the absorption 
spectra. Temperature in the probe was varied and regulated to within 50.5 "C of the 
desired value by heating nitrogen gas. Resonance frequency assignments were facilitated 
with the use of an acetyl chloride reference with an accuracy of 2 10 Hz. 
Over the 200-300K range studied there were three kinds of spectra for 3R1- 
TaS2(NH3)y3 which define three temperature domains. Evidence of the three domains 
were also found in the spectra of ~ R I I - T ~ S ~ ( N ~ H ~ ) ~ / ~  which were qualitatively the same 
as the spectra of ammonia intercalated 1T-TaS2. 
Two resonance lines were found in domain I (250-300 K). The resonance position 
of one was insensitive to crystal orientation in the magnetic field while the position of 
the other line was determined by the angle between the crystal c axis and static magnetic 
field vector H. The separation in frequency of the anisotropic and isotropic signals could 
be approximated by the relation 
v,- ~ = 1 . 5 A c o s 2 8  
where v, and y are line positions in Hz, 1.5 A is the maximum separation in Hz and 8 is 
the angle between the crystal c axis and H .  Shown in figure 1 are plots of (v, - q) versus 
8 for ammonia and hydrazine intercalated samples. These follow the (3 cos2 8 - 1)/2 
law for a Knight shift of K = A/56.1 PPM given in table 1. 
The ratio of intensities of the anisotropic to isotropic NMR absorption (raj) was also 
a feature that characterised each temperature domain. In domain I ,  rai was a constant of 
Letter to the Editor L277 
(deg) 
Figure 1. Frequency separation between the anisotropic and isotropic proton NMR lines in 
Hz versus 6 in degrees for 3RI-TaS2(NH3)~j3 (sample 1) and ~ R I I - T ~ S ~ ( N ~ H ~ ) ~ ~ ~ .  Full circles 
(0) show collected data with errors in frequency of 210Hz and in angle of 23". The full 
curve is the plot of 1.5 A cos26, where A is given in table 1. 
Table 1. Values of 1.5 A at 56.4 MHz (maximum separation in Hz of the anisotropic and 
isotropic lines) for different temperatures. 
Multiple lines 
Sample T > 2 5 0 K  2 5 0 K > T > 2 4 5 K  T < 2 4 5 K  AI/AIII 
(1) 640 530 300 130 110 260 2.46 
360 1.38 
55 3.63 
t ~ R I - T ~ S Z - ( N H ~ ) Q  2 6 (2) 5oo 400 220 90 - 
t 3RII-TaSz-(N2H4)4/3 t 6 (2) 200 - - - -  
+ The error 6 in stoichiometry is less than ten per cent of x 
the sample and not affected by variation of 8 or temperature. That A is proportional to 
the applied magnetic field was verified by carrying out measurements at Y = 56.4 and 
13.1 MHz. A representative spectrum of ~ R I - T ~ S Z ( N H ~ ) ~ ~  is shown in figure 2(a). 
In domain I1 (245-250 K) spectra of ?R1-TaS2(NH3)y3 were characterised by the 
presence of at least five lines; one isotropic: and three or four anisotropic. For each of the 
anisotropic absorptions, the separation from the isotropic line follows the A cos' 8 
behaviour. A representative spectrum for 8 = 0" is shown in figure 2(b). When all the 
lines collapse at 8 = 90°, the linewidth is equal to that of the isotropic line. As was 
observed in domain I ,  the rai values for all anisotropic lines were constants of the sample. 
For 3RII-TaS2(N2H4)4/3 there was an isotropic line and an unresolved manifold of several 
lines that collapsed at 8 = 90" showing a maximum separation at 8 = 0". 
In domain I11 (20g245 K) there were two lines which showed the orientational 
dependence observed in domain I. However, there was a striking feature in this tem- 
c9-c 
L278 Letter to the Editor 
L 
500 H z  
I 500 Hz I 
Figure 2. NMR absorption representative spectra of 3RI-TaS2(NH3)2;3 (sample 1). (a) At room 
temperature and e = 0". The anisotropic peak is at the right at higher frequency. The arrow 
is a 500 Hz standard and points to higher frequency. ( b )  At 250 K and 6' = 0". 
HO f o ~  ToSZ(NH3)2/3 
F 
Sample 1 Somple 2 
a b c d  
0' 2.60 0.62 0.73 0.33 1.35 
9 
P 
-0 
45' 
90' 
135" 
180' 2.29 0.27 0.89 2.41 1.88 
Figure 3. Illustration of how rotation of a sample cooled to a temperature below 245 K affects 
Tal,  the ratio of anisotropic to isotropic line intensity, for five different cooling cycles of 
sample 1 in table 1. A view down the instrument probe is shown to highlight the importance 
of the angle between the crystal c axis and the magnetic field. The crystal is seen edge-on 
and is pictured in an exaggerated off-axis position to help distinguish angles 0 = 0" and 
e =  180". 
Letter to the Editor L279 
perature domain which was not observed in domains I or 11. Each time any samples 
were cooled, r,, would take on randomly two new values that would reversibly intercon- 
vert as the crystal was rotated through 8 = 90" or 6 = 270". Figure 3 illustrates the change 
in Tal upon rotation and contains pairs of ra, values from several coolings. 
Our work shows that proton NMR of the guest molecules within TX2 is a good probe 
of the magnetic micro-environments within intercalated complexes. NMR reveals the 
presence of two micro-environments within the complexes as well as a phase transition 
at 245-250 K, most likely associated with the change in superlattice geometries observed 
in that temperature range by other methods. The significant observations are as follows: 
(i) Crystals intercalated with NH3 and N2H4 both show the same two-line pattern 
where the position of the low-frequency peak is independent of, and the high-frequency 
peak is dependent upon, the orientation of the crystal within the magnetic field. The 
proton linewidths observed are consistent with a rapid reorientation of NH3 and NzH4 
molecules within the layers. This is in agreement with the measurements made by 
Silbernagel and Gamble on 2H-TaS2(NH3),, but in this metallic complex the Knight 
shift is one order of magnitude greater than for the 3R-TaS21,. The different values of 
A reported in table 1 suggest that the proton Knight shift is determined by the number 
of adduct molecules in the complex which localises the electron states. 
(ii) Intercalant adduct molecules do not exchange between the two magnetic 
environments that are the source of the isotropic and anisotropic peaks as there is no 
evidence of exchange broadening or averaging. This means that the molecular complexes 
are stable within times longer than t = (2nA)-' or s. We offer the following 
proposal for the identities of the magnetic environments leading to the two lines. The 
isotropic signal arises from protons in fractured or poorly ordered domains and the 
anisotropic resonance is a result of adduct molecules occupying an ordered region where 
a superlattice exists. Fractures and other crystal defects that would prevent superlattice 
formation have been observed by a number of investigators (Tatlock and Acrivos 1978), 
and the intercalation process itself may be responsible for some of these faults. Regard- 
less of the cause of the crystal disorder, intercalant molecules in these disordered 
volumes would not be affected by fields oriented with the crystal geometry and, hence, 
give rise to the isotropic signal. 
(iii) Evidence for a role of superlattices in forming the anisotropic field is twofold. 
Wilson et a1 (1975) have measured bulk susceptibility in 1T-TaS2 and found variation of 
this parameter coincident with different superlattice geometries. Guy et a1 (1982) have 
observed similar effects in 3R-TaSz(NzH4),. Also we find a complex, multiline spectra 
with one line isotropic and the remainder anisotropic in the 245-250 K region. This is 
the same temperature range in which Tatlock and Acrivos (1978) observed a superlattice 
phase transition. In one of the materials we have studied, 3RII-TaS2(N2H4)4,3, our spectra 
suggest that two or more distinct superlattices may be present within the sample in this 
temperature range as each superlattice would contribute a different susceptibility field 
and be revealed as distinct anisotropic lines. 
(iv) Below 245 K, a two-line (anisotropic and isotropic) NMR signal like the room 
temperature spectra is found for ~ R I I - T ~ S Z ( N ~ H ~ ) ~ ~ ;  however, a smaller separation 
between the two lines is observed. This is in agreement with the fact that a different 
superlattice occurs within these crystals in the 20Cb245 K range (Tatlock and Acrivos 
1978) and that a decrease in carriers reduces the Knight shift. Also, in this temperature 
range, a new pattern of resonance line intensity is observed. The sum of anisotropic and 
isotropic line intensities is not altered from that value observed at room temperature, so 
to 
L280 Letter to the Editor 
the total number of protons in the sample remains constant within experimental uncer- 
tainty. Yet two discrete ratios of anisotropic to isotropic line intensities are found, one 
for each face of the crystal (figure 3), that do not change until the sample is warmed 
above 245 K. In addition, each cooling event yields a new pair of intensity ratios. The 
variation in intensities of the two peaks, which is not observed at temperatures above 
245 K, presents an interesting problem. To account for this particular situation, we 
propose a mechanism whereby the formation of the superlattice at low temperature is 
affected by temperature. Each cooling would appear to lead to varying amounts of this 
superlattice since crystal defects may be locked in or introduced by the temperature 
change. The anisotropic line intensity would be influenced by the volume of the crystal 
where the local magnetic fields cancel. While the temperature effects on relative line 
intensity are unpredictable, the effects of the magnetic field polarisation are not random. 
Although we are unable to explain this latter phenomenon, our results suggest that 
future experiments at higher magnetic fields may be able to shed some understanding 
on the chiral dependence of the NMR absorption below 245 K for samples cooled in a 
magnetic field. Transport measurements of samples cooled in a magnetic field may also 
show this chiral dependence if the above model where local magnetic fields cancel in 
discommensurate Bloch walls is correct. These were predicted by McMillan (1976) and 
found recently by TEM (Fung et a/ 1981). 
We have shown that proton NMR studies of the intercalant molecule with an octa- 
hedrally coordinated TaSz host are able to describe the phase transition near 245 K,  
which has not been observable by techniques based upon measurements of bulk proper- 
ties. Additionally, our findings suggest that intercalant adduct molecules such as 
ammonia and hydrazine are sensitive to local magnetic fields caused by superlattices. 
The physical significance is that the random potential fields in the adduct layer can affect 
the motion of electrons in the TaS2 layer. 
This work was supported in part by NSF DMR 790011 and NATO Grant 1441. J V 
Acrivos is grateful for a Visiting Fellowship at Trinity College, Cambridge during 1983 
and a Sabbatical leave from SJSU. We also thank Miss J Rowe who did the word 
processing at Trinity College. 
References 
Acrivos J V 1974 J .  Phys. Chem. 78 2399 
- 1979 PhysicsandChemistry of Materials witha Layer StructureVol. VI, ed. FLevy (Dordrecht :,Reidel). 
Acrivos J V, Parkin S S P, Reynolds J R, Code J and Marseglia E 1981 J .  Phys. C: Solid State Phys. 14 
Beal A R and Acrivos J V 1978 Phil. Mag. 37 409 
Bray D and Sauer E 1972 Solid State Commun .  11 1239 
Fung L, McKernan S,  Steeds J W and Wilson J A 1981 J .  Phys. C: Solid State Phys. 14 5417 
Gamble F and Silbernagel B 1975 J .  Chem. Phys. 63 2544 
Guy D P, Friend R H, Harrison M R, Johnson D C and Sienko M J 1982 J .  Phys. C: Solid State Phys. 15 L1245 
Hughes H P 1977 J .  Phys. C:  Solid State Phys. 10 L319 
McMillan E L 1976 Phys. Reu. B 14 1496 
Meyer S R, Howard R, Stewart G,  Acrivos J V and Geballe T H 1975 J .  Chem. Phys. 62 4411 
Sarma M, Beal A, Nulsen S and Friend R 1982 J .  Phys. C:  Solid State Phys. 15 477 
Tatlock G J and Acrivos J V 1978 Phil. Mag. 38 81 
Wilson J ,  Di Salvo F and Mahajan S 1975 Adu. Phys. 24 117 
pp 3>98 
L34Y-L357 


NMR measurements on intercalated 3R-TaS2.Ix (I=NH3 and N2H4)

San Jose State University

San Jose State University
SJSU ScholarWorks
Faculty Publications, Chemistry Chemistry
1-1-1984
NMR measurements on Intercalated 3R-TaS2.Ix
(I=NH3 and N2H4)
N. H. Handly
California Institute of Technology
Juana Vivó Acrivos
San Jose State University, juana.acrivos@sjsu.edu
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Recommended Citation
N. H. Handly and Juana Vivó Acrivos. "NMR measurements on Intercalated 3R-TaS2.Ix (I=NH3 and N2H4)" Journal of Physics C:
Solid State Physics (1984): L275-L280. doi:10.1088/0022-3719/14/19/007
J. Phys. C: Solid State Phys., 17 (1984) L275-L280. Printed in Great Britain 
LETTER TO THE EDITOR 
NMR measurements on intercalated 3R-TaS2 · lx 
(I = NH3 and N2H4)t 
N H Handly:j: and J V Acrivos§ 
+California Institute of Technology, Pasadena, CA91125, USA 
§ Trinity College, Cambridge, CB21TQ, UK 
Received 22 December 1983 
Abstract. Proton nuclear magnetic resonance was used to probe the environment of 
the intercalant molecule in low dimensional (aeolotropic) solids 3RI-TaSz(NHJhJ and 
3Ru-TaS2(N2H4)4/3. and, specifically to look for phase transitions associated with changes in 
superlattice geometry. The proton resonance frequency for the intercalated molecules in 
the temperature interval 200 to 300 K indicates that there are different magnetic environ­
ments in three temperature domains. (i) There is only one resonance field for molecules in 
isotropic magnetic environments. (ii) The high- and low-temperature domains (I and III) 
have molecules in only two different environments, whereas in the middle temperature 
domain (II) there are at least four different magnetic environments. (iii) The different 
magnetic environments measured by the ratio of anisotropic to isotropic resonance absorp­
tion intensity (r.,) indicate that the ratios r., are constants of the sample in domains I and II. 
(iv) At low temperatures (domain III), r,i depends on magnetic field polarisation effects and 
the temperature treatment of the sample. We conclude that the different magnetic environ­
ments observed for ammonia and hydrazine appear to be determined by the host. octahed­
rally coordinated TaS 2 . 
The phase transitions that are caused by the intercalation of low dimensional solids ( LDS) 
have important applications leading to new solid catalysts, conductors and battery 
materials. For this reason there has been recently a concentrated effort directed to 
determining the parameters which govern reaction (1): 
L(qh) + xl(g)- Llx(cpz) (1) 
where cp1 is the pristine initial crystal phase and cpz is the intercalated phase. This is a 
complex process which involves at least three steps. First Langmuir absorption of the 
adduct gas must occur; it is followed by chemisorption and finally insertion of the adduct 
in between the layers produces a phase transition. The understanding of reaction (1) 
was strengthened by spectroscopic (Beal and Acrivos 1978) and structural measurements 
by transmission electron microscopy (TEM) of N2H4in situ intercalated TaS2polymorphs. 
These indicate (Tatlock and Acrivos 1978) that the in-plane translational symmetry is 
reduced by intercalation in a precise way which depends on the solid and on the 
temperature and pressure. The periodic lattice distortion ( PLD) describes the dichalco­
genide by an empirical formula TyX2y with y ~ 3, where 103 formula units are held 
t This work is dedicated to Professor R W Vaughan of Cal. Tech., whose untimely death (1978) left a void 

that has not to this day been filled. The NMR work was done in his laboratory. 

§ To whom all correspondence is to be addressed. Permanent address: San Jose State University, San Jose, 

CA 95192, USA. 

0022-3719/84/090275 + 06 $02.25 © 1984 The Institute of Physics L275 
L276 Letter to the Editor 
together by layers of adduct I. The value of y is accurately determined from the PLD 
wavevectors which describe the Bloch functions of the partially occupied orbitally 
degenerate states of the metal or semimetal and give rise to the distortion according to 
the Jahn-Teller theorem (Hughes 1977, Acrivos 1974). The existence of localised 
electron states indicated by the PLD have led to transport and infrared spectroscopic 
measurements (Sarma et a/1982) which allow an estimate of a semiconductor energy 
gap of the order of half an electron volt in phase rn. The existence of localised para­
magnetic states was verified by ESR absorption measurements near 4.2 K (Guy et al 
1982). Nuclear magnetic resonance spectroscopy (NMR) and neutron diffraction offer 
another means for studying these intercalated solids. Both techniques have been used 
to probe the intercalant molecule and its macro-environment within the crystal, so far 
yielding information about the mobility of ammonia and the geometries of ammonia 
and pyridine in 2H-TaS2 (Gamble and Silbernagel1975, Bray and Sauer 1972). The NMR 
evidence suggests that the ammonia molecule is sensitive to phase changes associated 
with superlattice formation in intercalated 2H-TaS2• The ability to study phase behaviour 
in intercalated 1 T-TaS2 at a microscopic level would greatly add to our understanding 
of these materials. This work reports NMR studies of 3RrTaS2(NH3)2/3 and 
3RwTaS2(N2H4)4;3 between 200-300 K (Acrivos 1979, Acrivos et a/1981). 
The crystals of 1 T-TaS2 used in this work were grown by Meyer et at (1975) and A 
Beal and S N Nulsen (Sarma et a/1982). The NMR samples were prepared by placing a 
single crystal in a flattened tube to facilitate rotational studies which was then connected 
to a vacuum line for intercalation. Ammonia and hydrazine were purified prior to 
exposure to the crystals. Ammonia was condensed on sodium to remove traces of water 
and then the gas was admitted to the sample. Freeze-dried hydrazine was distilled in situ 
and then admitted to the sample. The ammonia pressure was 700 Torr and the hydrazine 
vapour pressure was 12 Torr. After one week at room temperature, the sample tube 
was immersed in liquid nitrogen and the tube sealed by melting the glass. 
The spectra were collected at 56.4 and 13.1 MHz. Free induction decays were 
collected for time averaging and were then Fourier transformed to give the absorption 
spectra. Temperature in the probe was varied and regulated to within ±0.5 oc of the 
desired value by heating nitrogen gas. Resonance frequency assignments were facilitated 
with the use of an acetyl chloride reference with an accuracy of± 10Hz. 
Over the 200-300 K range studied there were three kinds of spectra for 3Rr 
TaS2(NH3) 213 which define three temperature domains. Evidence of the three domains 
were also found in the spectra of 3Rn-TaS2(N2H4)4;3 which were qualitatively the same 
as the spectra of ammonia intercalated 1 T-TaS2 . 
Two resonance lines were found in domain I (250-300 K). The resonance position 
of one was insensitive to crystal orientation in the magnetic field while the position of 
the other line was determined by the angle between the crystal c axis and static magnetic 
field vector H. The separation in frequency of the anisotropic and isotropic signals could 
be approximated by the relation 
v. - v; = 1. 5 A cos2 8 
where v. and V; are line positions in Hz, 1.5 A is the maximum separation in Hz and 8 is 
the angle between the crystal c axis and H. Shown in figure 1 are plots of ( v.- Vi) versus 
efor ammonia and hydrazine intercalated samples. These follow the (3 cos2 8- 1)/2 
law for a Knight shift of K = A/56.1 PPM given in table 1. 
The ratio of intensities of the anisotropic to isotropic NMR absorption (r.;) was also 
a feature that characterised each temperature domain. In domain/, ra; was a constant of 
600 
-;:; 
~ 
300 
200 
100 
-30 30 120 
200 
100 
40 120 180 
(deg) 
Letter to the Editor L277 
Figure 1. Frequency separation between the anisotropic and isotropic proton NMR lines in 
Hz versus 8 in degrees for 3R1-TaS2(NH3)v3 (sample 1) and 3Rn-TaS2(NlH4)4;J. Full circles 
(e) show collected data with errors in frequency of ±10Hz and in angle of ±3°. The full 
curve is the plot of 1.5 A cos28, where A is given in table 1. 
Table 1. Values of 1.5 A at 56.4 MHz (maximum separation in Hz of the anisotropic and 
isotropic lines) for different temperatures. 
Multiple lines 
Sample T > 250 K 250 K > T > 245 K 
(1) 640 530 300 130 110 260 2.46 t 3R1-TaS2-(NH3)l/3 ± b ( )2 500 400 220 90 360 1.38 
t 3Rn-TaS2-(N2H4)4!3 ± b (2) 200 55 3.63 
t The error bin stoichiometry is less than ten per cent of x. 
the sample and not affected by variation of 8 or temperature. That A is proportional to 
the applied magnetic field was verified by carrying out measurements at v = 56.4 and 
13.1 MHz. A representative spectrum of 3R1-TaSz(NH3)2/3 is shown in figure 2(a). 
In domain II (245-250 K) spectra of 3R1-TaSz(NH3)2/3 were characterised by the 
presence of at least five lines; one isotropi<.: and three or four anisotropic. For each of the 
anisotropic absorptions, the separation from the isotropic line follows the A cos2 8 
behaviour. A representative spectrum for 8 = oo is shown in figure 2(b). When all the 
lines collapse at 8 = 90°, the linewidth is equal to that of the isotropic line. As was 
observed in domain I, the '•i values for all anisotropic lines were constants of the sample. 
For 3Ru-TaS2(N2H4)4/3 there was an isotropic line and an unresolved manifold of several 
lines that collapsed at 8 = 90° showing a maximum separation at 8 = 0°. 
In domain III (200-245 K) there were two lines which showed the orientational 
dependence observed in domain I. However, there was a striking feature in this tern­
C9-C 
L278 Letter to the Editor 
(a) 
-­500Hz 
(b) 
500Hz 
Figure 2. NMR absorption representative spectra of 3RI-TaS2(NH3)213(sample 1). (a) At room 
temperature and e= 0°. The anisotropic peak is at the right at higher frequency. The arrow 
is a 500Hz standard and points to higher frequency. (b) At 250 K and e= 0°. 
Ho rai TaS2(NH3I213 
Sample 1 Sample 2 
o-o· a 2 60 b 0.62 0.73 d 0.33 1.35 
45° 
90" 
135° 
180" 2.29 0.27 0.89 2.41 1.88 
Figure 3. Illustration of how rotation of a sample cooled to a temperature below 245 K affects 
rat, the ratio of anisotropic to isotropic line intensity, for five different cooling cycles of 
sample 1 in table 1. A view down the instrument probe is shown to highlight the importance 
of the angle between the crystal c axis and the magnetic field. The crystal is seen edge-on 
and is pictured in an exaggerated off-axis position to help distinguish angles e= oo and 
e= 180°. 
Letter to the Editor L279 
perature domain which was not observed in domains I or II. Each time any samples 
were cooled, rai would take on randomly two new values that would reversibly intercon­
vert as the crystal was rotated through e= 90° ore= 270°. Figure 3 illustrates the change 
in rai upon rotation and contains pairs of rai values from several coolings. 
Our work shows that proton NMR of the guest molecules within TX2 is a good probe 
of the magnetic micro-environments within intercalated complexes. NMR reveals the 
presence of two micro-environments within the complexes as well as a phase transition 
at 245-250 K, most likely associated with the change in superlattice geometries observed 
in that temperature range by other methods. The significant observations are as follows: 
(i) Crystals intercalated with NH3 and N2H4 both show the same two-line pattern 
where the position of the low-frequency peak is independent of, and the high-frequency 
peak is dependent upon, the orientation of the crystal within the magnetic field. The 
proton linewidths observed are consistent with a rapid reorientation of NH3and N2H4 
molecules within the layers. This is in agreement with the measurements made by 
Silbernagel and Gamble on 2H-TaSz(NH3)x, but in this metallic complex the Knight 
shift is one order of magnitude greater than for the 3R-TaS2Ix. The different values of 
A reported in table 1 suggest that the proton Knight shift is determined by the number 
of adduct molecules in the complex which localises the electron states. 
(ii) Intercalant adduct molecules do not exchange between the two magnetic 
environments that are the source of the isotropic and anisotropic peaks as there is no 
evidence ofexchange broadening or averaging. This means that the molecular complexes 
are stable within times longer than t = (2.rrA)- 1 or 10-3to 10-4s. We offer the following 
proposal for the identities of the magnetic environments leading to the two lines. The 
isotropic signal arises from protons in fractured or poorly ordered domains and the 
anisotropic resonance is a result of adduct molecules occupying an ordered region where 
a superlattice exists. Fractures and other crystal defects that would prevent superlattice 
formation have been observed by a number of investigators (Tatlock and Acrivos 1978), 
and the intercalation process itself may be responsible for some of these faults. Regard­
less of the cause of the crystal disorder, intercalant molecules in these disordered 
volumes would not be affected by fields oriented with the crystal geometry and, hence, 
give rise to the isotropic signal. 
(iii) Evidence for a role of superlattices in forming the anisotropic field is twofold. 
Wilson et al (1975) have measured bulk susceptibility in 1 T-TaS 2 and found variation of 
this parameter coincident with different superlattice geometries. Guy et al (1982) have 
observed similar effects in 3R-TaS2(NzH4)x· Also we find a complex, multiline spectra 
with one line isotropic and the remainder anisotropic in the 245-250 K region. This is 
the same temperature range in which Tatlock and Acrivos (1978) observed a super lattice 
phase transition. In one ofthe materials we have studied, 3Rn-TaSz(N2H4)4;3, our spectra 
suggest that two or more distinct superlattices may be present within the sample in this 
temperature range as each superlattice would contribute a different susceptibility field 
and be revealed as distinct anisotropic lines. 
(iv) Below 245 K, a two-line (anisotropic and isotropic) NMR signal like the room 
temperature spectra is found for 3Rn-TaS2(N2H4)4;3; however, a smaller separation 
between the two lines is observed. This is in agreement with the fact that a different 
superlattice occurs within these crystals in the 200-245 K range (Tatlock and Acrivos 
1978) and that a decrease in carriers reduces the Knight shift. Also, in this temperature 
range, a new pattern of resonance line intensity is observed. The sum of anisotropic and 
isotropic line intensities is not altered from that value observed at room temperature, so 
L280 Letter to the Editor 
the total number of protons in the sample remains constant within experimental uncer­
tainty. Yet two discrete ratios of anisotropic to isotropic line intensities are found, one 
for each face of the crystal (figure 3), that do not change until the sample is warmed 
above 245 K. In addition, each cooling event yields a new pair of intensity ratios. The 
variation in intensities of the two peaks, which is not observed at temperatures above 
245 K, presents an interesting problem. To account for this particular situation, we 
propose a mechanism whereby the formation of the superlattice at low temperature is 
affected by temperature. Each cooling would appear to lead to varying amounts of this 
superlattice since crystal defects may be locked in or introduced by the temperature 
change. The anisotropic line intensity would be influenced by the volume of the crystal 
where the local magnetic fields cancel. While the temperature effects on relative line 
intensity are unpredictable, the effects of the magnetic field polarisation are not random. 
Although we are unable to explain this latter phenomenon, our results suggest that 
future experiments at higher magnetic fields may be able to shed some understanding 
on the chiral dependence of the NMR absorption below 245 K for samples cooled in a 
magnetic field. Transport measurements of samples cooled in a magnetic field may also 
show this chiral dependence if the above model where local magnetic fields cancel in 
discommensurate Bloch walls is correct. These were predicted by McMillan (1976) and 
found recently by TEM (Fung et a/1981). 
We have shown that proton NMR studies of the intercalant molecule with an octa­
hedrally coordinated TaS2 host are able to describe the phase transition near 245 K, 
which has not been observable by techniques based upon measurements of bulk proper­
ties. Additionally, our findings suggest that intercalant adduct molecules such as 
ammonia and hydrazine are sensitive to local magnetic fields caused by superlattices. 
The physical significance is that the random potential fields in the adduct layer can affect 
the motion of electrons in the TaSzlayer. 
This work was supported in part by NSF DMR 790011 and NATO Grant 1441. J V 
Acrivos is grateful for a Visiting Fellowship at Trinity College, Cambridge during 1983 
and a Sabbatical leave from SJSU. We also thank Miss J Rowe who did the word 
processing at Trinity College. 
References 
Acrivos J V 1974 J. Phys. Chern. 78 2399 
- 1979 Physics and Chemistry ofMaterials with a Layer Structure Vol. VI, ed. FLevy (Dordrecht :Reidel). 
pp 33-98 
Acrivos J V, ParkinS S P, Reynolds J R, Code J and Marseglia E 1981 J. Phys. C: Solid State Phys. 14 
L34~L357 
Beal A Rand Acrivos J V 1978 Phil. Mag. 37 409 
Bray D and Sauer E 1972 Solid State Commun. 111239 
Fung L, McKernan S, Steeds J Wand Wilson J A 1981 J. Phys. C: Solid State Phys. 14 5417 
Gamble F and Silbernagel B 1975 J. Chern. Phys. 63 2544 
GuyD P, Friend RH, Harrison M R, Johnson D Cand Sienko MJ1982J. Phys. C: Solid State Phys. 15 L1245 
Hughes H P 1977 J. Phys. C: Solid State Phys. 10 L319 
McMillan E L 1976 Phys. Rev. B 14 1496 
MeyerS R, Howard R, Stewart G, Acrivos J V and Geballe T H 1975 J. Chern. Phys. 62 4411 
Sarma M, Beal A, Nulsen Sand Friend R 1982 J. Phys. C: Solid State Phys. 15 477 
Tatlock G J and Acrivos J V 1978 Phil. Mag. 38 81 
Wilson J, DiSalvo F and Mahajan S 1975 Adv. Phys. 24 117 


Solid State Phys. 14 Beal A R and Acrivos

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NMR measurements on intercalated 3R-TaS2.Ix (I=NH3 and N2H4)

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